Fourth Grade Links

Language Arts
www.starfall.com
http://www.bbc.co.uk/schools/websites/4_11/topic/literacy.shtml (great kid friendly links that teach specific skills, great for review, Pre-K through 12)

Math
http://www.bbc.co.uk/schools/websites/4_11/topic/numeracy.shtml (see above comment re: www.bbc.co.uk)
www.aaamath.com
www.funbrain.com
www.multiplication.com

Social Studies

Science

Music and Art
http://www.bbc.co.uk/northernireland/schools/4_11/music/mm/ (nice reading comprehension component)